RADIAL SHOOTS. MECHANICAL HYPOTHESIS OF LEAF-POSITION 79 



point where the transition takes place from the region of the foliage-leaves to the 

 region of the flower, or if these organs remain equally large whilst the common 

 axis increases in circumference, changes of position will take place which conform 

 in all essentials with the displacement brought about by longitudinal pressure; the 

 only difference being that the changes which in the 

 latter case must affect the same organs one after the 







other are here observed in different organs beside one 

 another. 



Fig. 35 gives a representation of the effect of P 

 gradual decrease in size of organs having a circular 

 outline in cross-section. In the lower part of the 

 figure, at A the third and fifth rows are in contact and 

 cut one another at about a right angle ; at B the fifth 

 and eighth parastichies do this ; whilst at C the eighth B 

 and thirteenth touch one another but cut at an oblique 

 angle. Between these we find at n and /3 positions of 

 transition in which the organs are in contact in three 

 directions. The rows thus come to occupy quite the 

 same position and therefore to have the same diverg- 

 ences as we have already noticed in the displacement 

 of organs of equal size in consequence of predominant 

 growth in thickness of a mother-organ. 



If the organs become small very rapidly, group- 

 ings may arise which require special consideration. 

 According to the degree of diminution links are " 

 obtained which Schwendener has designated first, 

 second, and third transition-figures. Cases of the third 

 kind are very rare in the plant-kingdom and we shall 

 confine ourselves therefore to an account of the first 

 and second only. Fig. 36 gives a representation of 

 the first transition-figure. In the space bounded by 

 the lower three ellipses an organ appears which 

 touches two of the ellipses, whilst a third organ stands 

 in contact with it and the third ellipse. According 

 to the numbering of the ellipses which has been 

 chosen in the figure the contact ceases in the fifth 

 row, and is renewed in the thirteenth row. In the 

 case of the second transition-figure represented in 

 Fig. 37, two organs appear in the space but do not FlG - 35- Scheme to exhibit the con- 



" _ sequence of the gradual decrease in size 



Completely fill it Up, SO that a third Organ Can appear of cylindric organs. After Schwendener. 



between these but it does not touch the lowermost 



ellipse. The numbers of the ellipses in this figure show that the contact ceases here 

 both in the fifth and in the eighth row but is renewed in the thirteenth and twenty-first. 

 In the advance of the contact-lines here an entire step of the intermediate positions 

 is skipped over. It fits in to a certain extent with the position at A in Fig. 35, 



